http://www.hindawi.comThe latest articles from Hindawi Publishing Corporation© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/275357The dynamic performance of wide-bandgap 4H-SiC based double drift region (p++ p n n++) IMPATT diode is simulated for the first time at terahertz frequency (0.7 Terahertz) region. The simulation experiment establishes the potential of SiC based IMPATT diode as a high power (2.5×1011 Wm−2) terahertz source. The parasitic series resistance in the device is found to reduce the RF power output by 10.7%. The effects of external radiation on the simulated diode are also studied. It is found that (i) the negative conductance and (ii) the negative resistance of the diode decrease, while, the frequency of operation and the quality factor shift upward under photoillumination. Holes in 4H-SiC based IMPATT are found to dominate the modulation activities. The inequality in the magnitude of electron and hole ionization rates in the semiconductors may be correlated with these findings.Moumita Mukherjee, Nilratan Mazumder, and Sitesh Kumar Roy© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/859052To explain the relevant changes in the electron cyclotron resonance ion source behaviour for small variations of the exciting radiation frequency, we determine the spatial distribution of the field within the cavity for every resonant mode.Fabrizio Consoli, Luigi Celona, Giovanni Ciavola, Santo Gammino, Fabio Maimone, Rocco Salvatore Catalano, Sebastiano Barbarino, David Mascali, and Livia Tumino© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/134805Silicon-based radio-frequency integrated circuits are becoming more and more competitive in wide-band frequency range. An essential component of these ICs is on-chip (integrated) transformer. It is widely used in mobile communications, microwave integrated circuits, low-noise amplifiers, active mixers, and baluns. This paper deals with the design, simulation, and analysis of novel fractal configurations of the primary and secondary coils of the integrated transformers. Integrated stacked transformers, which use fractal curves (Hilbert, Peano, and von Koch) to form the primary and secondary windings, are presented. In this way, the occupied area on the chip is lower and a number of lithographic processes are decreased. The performances of the proposed integrated transformers are investigated with electromagnetic simulations up to 20 GHz. The influence of the order of fractal curves and the width of conductive lines on the inductance and quality factor is also described.Goran Stojanović, Milan Radovanović, and Vasa Radonić© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2007/80839Yalin Lu, Weili Zhang, and Min Qiu© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/816969An E-field probe has been developed for EMC immunity tests performed in closed space. The leads are flexible resistive transmission lines. Their influence on the field distribution is negligible. The probe has an isotropic reception from 100 MHz to 18 GHz; the sensitivity is in the 3 V/m–10 V/m range. The device is an accessory of the EMC test chamber. The readout of the field magnitude is carried out by personal computer, which fulfils also the required corrections of the raw data.Béla Szentpáli, István Réti, Ferenc B. Molnár, János Farkasvölgyi, Károly Kazi, Zoltán Mirk, Aurél Sonkoly, and Zoltán Horváth© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2007/24084Transmission metallic gratings having the shape of converging-diverging channel (CDC) give an extra degree of freedom to exhibit enhanced transmission resonances. By varying the gap size at the throat of CDC, the spectral locations of the transmission resonance bands can be shifted close to each other and have high transmittance in a very narrow energy band. Hence, the CDC shape metallic gratings can lead to almost perfect transmittance for any desired wavelength by carefully optimizing the metallic material, gap at the throat of CDC, and grating parameters. In addition, a cavity surrounded by the CDC shaped metallic grating and a one-dimensional (1D) photonic crystal (PhC) can lead to an enhanced emission with properties similar to a laser. The large coherence length of the emission is achieved by exploiting the coherence properties of the surface waves on the gratings and PhC. The new multilayer structure can attain the spectral and directional control of emission with only p-polarization. The resonance condition inside the cavity is extremely sensitive to the wavelength, which would then lead to high emission in a very narrow wavelength band. Such simple 1D multilayer structure should be easy to fabricate and have applications in photonic circuits, thermophotovoltaics, and potentially in energy efficient incandescent sources.Arvind Battula, Yalin Lu, R. J. Knize, Kitt Reinhardt, and Shaochen Chen© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/247171The voltage-mode universal biquadratic filter and sinusoidal quadrature oscillator based on the use of current differencing buffered amplifiers (CDBAs) as active components have been proposed in this paper. All the proposed configurations employ only two CDBAs and six passive components. The first proposed CDBA-based biquad configuration can realize all the standard types of the biquadratic functions, that is, lowpass, bandpass, highpass, bandstop, and allpass, from the same topology, and can also provide orthogonal tuning of the natural angular frequency (ωo) and the bandwidth (BW) through separate virtually grounded passive components. By slight modification of the first proposed configuration, the new CDBA-based sinusoidal quadrature oscillator is easily obtained. The oscillation condition and the oscillation frequency are independently adjustable by different virtually grounded resistors. The sensitivity analysis of all proposed circuit configurations is shown to be low. PSPICE simulations and experimental results based upon commercially available AD844-type CFAs are included, which confirm the workability of the proposed circuits.Worapong Tangsrirat, Tattaya Pukkalanun, and Wanlop Surakampontorn© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2007/93548A design of parallel-coupled microstrip bandpass filters without spurious resonance is presented. Two different techniques are used to eliminate this response at twice the passband frequency (2fo). The first one is based on usage of suspended substrate, while the second is carried out by shorting the parallel-coupled lines to the ground plane through two shorting walls. The numerical results show that a broadband filter can be obtained by the suppression of the spurious response. The finite difference time domain (FDTD) with the perfect matched layer (PML) is used in the present analysis. The obtained results are compared with the available published data and good agreements are found.Maher M. Abd-Elrazzak© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2007/59856An approach for the fault diagnosis of single and multiple faults in linear analog electronic circuits is proposed in this paper. The simulation-before-test (SBT) diagnosis approach proposed in this write up basically consists of obtaining the frequency response of fault free/faulty circuit. The peak frequency and the peak amplitude from the error response are observed and processed suitably to extract distinct signatures for faulty and nonfaulty conditions under maximum tolerance conditions for other network components. The artificial neural network classifiers are then used for the classification of fault. Networks of reasonable dimensions are shown to be capable of robust diagnosis of analog circuits including effects due to tolerances. This is a unique contribution of this paper. Fault computation time is drastically reduced from the traditional analysis techniques. This results in a direct dollar savings at test time. A comparison of the proposed work with the previous works which also employ preprocessing techniques, reveals that our algorithm performs significantly better in fault diagnosis of analog circuits due to our proposed preprocessing techniques.V. Manikandan and N. Devarajan© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2007/63139This paper presents a fully experimental and theoretical study on transmission properties of a deep metallic grating with subwavelength slits in THz frequency region by using THz time domain spectroscopy (THz-TDS). The grating exposed to p-polarized incident wave exhibits enhanced nonresonant transmission in the long-wavelength region where the incident wavelength is larger than the grating period. Wood anomalies are observed when the wavelength is comparable to the grating period. Strict theory is given to explain the experimental results and the two are in good agreement. It is proposed that the Wood dips may be considered a criterion and a tool to judge and control the uniformity or fabricating accuracy of the grating period.Dong Liang, Qirong Xing, Zhen Tian, Changlei Wang, Weili Zhang, Jianqiang Gu, Yanfeng Li, Lu Chai, Qingyue Wang, and Aleksei Zheltikov© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2007/40249We present a review of experimental studies of resonant excitation of terahertz surface plasmons in two-dimensional arrays of subwavelength metal holes. Resonant transmission efficiency higher than unity was recently achieved when normalized to the area occupied by the holes. The effects of hole shape, hole dimensions, dielectric function of metals, polarization dependence, and array film thickness on resonant terahertz transmission in metal arrays were investigated by the state-of-the-art terahertz time-domain spectroscopy. In particular, extraordinary terahertz transmission was demonstrated in arrays of subwavelength holes made even from Pb, a generally poor metal, and having thickness of only one-third of skin depth. Terahertz surface plasmons have potential applications in terahertz imaging, biosensing, interconnects, and development of integrated plasmonic components for terahertz generation and detection.Weili Zhang, Abul K. Azad, and Jiaguang Han© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2007/15754The plasma clean in a plasma-enhanced chemical vapor deposition (PECVD) system plays an important role to ensure the same chamber condition after numerous film depositions. The periodic and applicable plasma clean in deposition chamber also increases wafer yield due to less defect produced during the deposition process. In this study, the plasma clean rate (PCR) of silicon oxide is investigated after the silicon nitride deposited on Cu and silicon oxide substrates by remote plasma system (RPS), respectively. The experimental results show that the PCR drastically decreases with Cu substrate compared to that with silicon oxide substrate after numerous silicon nitride depositions. To understand the substrate effect on PCR, the surface element analysis and bonding configuration are executed by X-ray photoelectron spectroscopy (XPS). The high resolution inductively coupled plasma mass spectrometer (HR-ICP-MS) is used to analyze microelement of metal ions on the surface of shower head in the PECVD chamber. According to Cu substrate, the results show that micro Cu ion and the CuOx bonding can be detected on the surface of shower head. The Cu ion contamination might grab the fluorine radicals produced by NF3 ddissociation in the RPS and that induces the drastic decrease on PCR.Shiu-Ko JangJian and Ying-Lang Wang© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2007/17692A new structural engineering strategy is introduced for optimizing the fabrication of arrayed nanorod materials, optimizing superlattice structures for realizing a strong coupling, and directly developing nanophotonic devices. The strategy can be regarded as “combinatorial” because of the high efficiency in optimizing structures. In this article, this strategy was applied to grow ZnO nanorod arrays, and to develop a new multifunctional photodetector using such nanorod arrays, which is able to simultaneously detect power, energy, and polarization of an incident ultraviolet radiation. The strategy was also used to study the extraordinary dielectric behavior of relaxor ferroelectric lead titanate doped lead magnesium niobate heterophase superlattices in the terahertz frequencies, in order to investigate their dielectric polariton physics and the potential to be integrated with tunable surface resonant plasmonics devices. Yalin Lu© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2007/30946The coupling of light to collective oscillation of electrons on the metal surface allows the creation of surface plasmon-polariton wave. This surface wave is of central interest in the field of plasmonics. In this paper, we will present a brief review of this field, focusing on the plasmonic waveguide and plasmonic transmission. In the plasmonic waveguide, the light can be guided along the metal surface with subwavelength lateral dimensions, enabling the possibility of high-density integration of the optical elements. On the other hand, in the plasmonic transmission, the propagation of light through a metal surface can be tailored with the subwavelength holes, leading to the anomalous transmission behaviors which have received extensive investigations in recent years. In addition, as a supplement to plasmonics in the visible and near-infrared region, the study of THz plasmonics has also been discussed.Cheng-Ping Huang and Yong-Yuan Zhu© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2007/49691The properties of planar, single-layer metamaterials, or metafilms, are studied by varying the structural components of the split-ring resonators used to comprise the overall medium. Measurements and simulations reveal how minor design variations in split-ring resonator structures can result in significant changes in the macroscopic properties of the metafilm. A transmission-line/circuit model is also used to clarify some of the behavior and design limitations of the metafilms. Though our results are illustrated in the terahertz frequency range, the work has broader implications, particularly with respect to filtering, modulation, and switching devices.John F. O'Hara, Evgenya Smirnova, Abul K. Azad, Hou-Tong Chen, and Antoinette J. Taylor© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2007/52461Surface-plasmon-polariton (SPP) waveguides made of materials available in nature have, in general, been found to suffer from very high absorption loss when light confinement is beyond diffraction limit. In this paper, the possibility of combining both the conventional index-guiding and the SPP-guiding mechanisms together into one single waveguide is being explored. Such waveguides, expectedly, inherent the low-loss feature of all-dielectric waveguides as well as the superior mode field confinement possessed by SPP waveguides. By using experimentally ready materials, it is theoretically shown that compact metallodielectric waveguides can be designed with a ∼500×500 nm2 core size around the 1550 nm telecommunication wavelength. The examined waveguides can be interpreted as a gap SPP waveguide with an inner dielectric core. Compared to pure SPP waveguides, such hybrid waveguides have a comparable mode field size, but with significantly lower loss (∼0.05 dB/μm for either quasi-TE or quasi-TM operation). Therefore they can be potentially deployed for a range of integrated photonic applications.Min Yan and Min Qiu© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2007/78602Counter-directional coupling between subwavelength-diameter silica wire and single-line-defect two-dimensional photonic crystal slab waveguide is studied numerically using parallel three-dimensional finite-different time-domain method. By modifying silica wire properties or engineering photonic crystal waveguide dispersion band, the coupling central wavelength can be moved to the slow light region and the coupling efficiency improves simultaneously. One design gives 82% peak power transmission from silica wire to photonic crystal waveguide over an interacting distance of 50 lattice constants. The group velocity is estimated as 1/35 of light speed in vacuum.Ziyang Zhang, Ulf Andersson, and Min Qiu© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2007/36849This article presents a dual-mode (voltage-mode and current-mode) universal biquadratic filter performing completely standard functions: lowpass, highpass, bandpass, band-reject, and allpass functions, based on plus-type dual-output second-generation, current controlled, current conveyor (DO-CCCII+). The features of the circuit are that the bandwidth and natural frequency can be tuned electronically via the input bias currents: the circuit description is very simple, consisting of merely 2 DO-CCCIIs and 2 capacitors: the circuit can provide either the voltage-mode or current-mode filter without changing circuit topology. Additionally, each function response can be selected by suitably selecting input signals with digital method. Without any external resistors, the proposed circuit is very suitable to further develop into an integrated circuit. The PSPICE simulation results are depicted. The given results agree well with the theoretical anticipation. The maximum power consumption is approximately 1.81 mW at ±1.5 V supply voltages.M. Siripruchyanun and W. Jaikla© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2007/17846Poly(o-toluidine) (POT) thin films were synthesized by electrochemical polymerization under cyclic voltammetric conditions from o-toluidine monomer in an aqueous solution of HCl as a supporting electrolyte. The electrosynthesized films were characterized by UV-Visible, FT-Raman, and FTIR spectroscopies. The optical transmissions of the as-deposited films were measured in the 400–900 nm wavelength range. These measurements showed that the optical band gap of the polymer films is in the order of 2.52 eV. The FT-Raman and FTIR measurements showed that the POT film is composed of imine and amine units. ITO/POT/Al devices were fabricated by thermal evaporation of aluminum circular contacts on films deposited on ITO-coated glass. The nonlinear current-voltage characteristics of these devices indicate a rectifying behavior. The diode parameters were calculated from I-V characteristics using the modified Shockley equation. The measured C-V and C-F characteristics are presented.A. Elmansouri, A. Outzourhit, A. Oueriagli, A. Lachkar, N. Hadik, M. E. Achour, A. Abouelaoualim, K. Berrada, and E. L. Ameziane© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2007/92034New current-mode bandpass filters using three single outputs inverting second generation current conveyors (ICCII) are introduced. The first circuit uses two ICCII+ and one ICCII−, and realizes an inverting bandpass response. This circuit has one floating resistor and no independent gain control. The second circuit uses three ICCII− and realizes a noninverting bandpass response. The third circuit uses three ICCII+ and realizes also a noninverting bandpass response. The second and third circuits employ four grounded resistors and two grounded capacitors and have independent control on Q and on the center frequency gain by varying a single grounded resistor. Spice simulation results using 0.5 um CMOS transistors are included to support the theoretical analysis.Ahmed M. Soliman© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2007/69515This paper details the design of integrated balanced PSK modulator using finline coplanar line hybrid junction. The PSK signal output is in suspended stripline with incident wave carrier in finline. Schottky barrier Diode MA4E2037 has been used for modulation. The balanced configuration offers high isolation between the carrier input port and the modulated carrier output port and thus the pulse width variations and amplitude deviations are suppressed. An insertion loss imbalance of ±1.5 dB with an average loss of 2 dB in the two switching states has been achieved over 38.9 to 40 GHz. The phase imbalance is ±10 degrees with phase switching from 180 to 199 degrees As the PSK output signal is in suspended stripline, two BPSK modulators can be easily combined together to work as QPSK modulator.Ashok Mittal and Asok De© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2001/10595In this paper, the electric conductivity of carbon nanotubes is investigated by deriving a mathematical expression for the quantized conductance in an ideal one-dimensional potential well with a single electron moving in it. Our results are compared with experimental data.M. A. Grado-Caffaro and M. Grado-Caffaro© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2001/18731In this paper, we present a drain current model for stressed short-channel MOSFET's. Stress conditions are chosen so that the interface states generated by hot-carriers are dominant. The defects generated during stress time are simulated by a spatio-temporal gaussian distribution. The parasitic source and drain resistances are included. We also investigate the impact of the interface charge density, generated during stress, on the transconductance. Simulation results show a significant degradation of the drain current versus stress time.R. Marrakh and A. Bouhdada© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2001/23505In this paper, we propose a very simple and efficient binary run-length compression technique for non-binary sources. The technique is based on mapping the non-binary information source into an equivalent binary source using a new fixed-length code instead of the ASCII code. The codes are chosen such that the probability of one of the two binary symbols; say zero, at the output of the mapper is made as small as possible. Moreover, the “all ones” code is excluded from the code assignments table to ensure the presence of at least one “zero” in each of the output codewords. Compression is achieved by encoding the number of “ones” between two consecutive “zeros” using either a fixed-length code or a variable-length code. When applying this simple encoding technique to English text files, we achieve a compression of 5.44bits/character and 4.6bits/character for the fixed-length code and the variablelength (Huffman) code, respectively.Abdel-Rahman Jaradat and Mansour I. Irshid© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2001/27076A new active-only sinusoidal oscillator is presented. The oscillator circuit uses two internally compensated operational amplifiers, two plus-type second-generation current conveyors and three operational transconductance amplifiers. The proposed circuit enjoys the attractive features of totally uncoupled frequency and condition of oscillation, low sensitivities, electronic tunability and integratability.Muhammad Taher Abuelmaatti© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2001/29392A new S-shaped negative differential resistance (NDR) switching device, prepared by molecular beam epitaxy (MBE), has been successfully developed in a GaAs double triangular barrier structure. Symmetrical bidirectional S-shaped NDR characteristics are observed experimentally. The bidirectional current-voltage (I–V) characteristics exhibit a new type of NDR caused by an avalanche multiplication process in reverse biased base-collector region and barrier redistribution. Under a base current injection with respect to the cathode, the device exhibits a conventional transistor with a current gain of 1.2 at room temperature. The experimentally electrical results can be easily understood by an equivalent circuit. In addition, a new optoelectronic switching device is also proposed which may have the potential for bidirectional wave length emission. M. R. Lef, K. F. Yarn, C. C. Chen, and W. R. Chang© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2001/34065In order to characterise the velocity saturation phenomena in short channel MOSFET's, a simple method is proposed in this work. It is based on the comparison between transistor behaviour in ohmic and saturation regime respectively. Therefore, the MOSFET characteristic Id0(Vd). avoiding velocity saturation phenomena, can be obtained from ohmic characteristic Id(Vg) and compared with the experimental characteristic Id(Vd).A. El Abbassi, Y. Amhouche, K. Raïs, and R. Rmaily© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2001/37629In this paper, the dependence on the partial pressure of oxygen of the shift in the energy band-gap of CdO thin films for the visible region is investigated from the theoretical point of view on an experimental basis. In our analysis, the role played by the dependence of the carrier density upon the above pressure is emphasized.M. A. Grado-Caffaro, M. Grado-Caffaro, and S. L. Sapienza© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2001/41403This paper presents an efficient and accurate Monte-Carlo approach to the problem of estimating average node switching probabilities in sequential circuits, which are used in average power estimation and reliability analysis of these circuits. Specific error bounds for the proposed estimation method are given at a certain level of confidence. This method is based on the analysis of paths in the State Transition Graph (STG) of the circuit and is validated by both theoretical analysis as well as experimental results.Georgios I. Stamoulis© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2001/45964This paper examines the impact of asymmetric pulses in NRZ waveforms generated by maximum-length sequences and used in spread spectrum systems. The data asymmetry phenomenon is produced by differential propagation delays through logic circuits in the payloads. A model of three elementary pulse shapes is employed to characterize the signal source and the occurrence probabilities for each is calculated. The autocorrelation function of the waveform is eventually obtained taking into account the asymmetry, and some numerical evaluations are finally presented to show the deviation from the theoretic case where no asymmetry is considered.A. P. Papavasileiou and C. N. Capsalis© 2008, Hindawi Publishing Corporation. All rights reserved.